In supporting machine parts, which rotate on a pin or the like which as a rule is stationary, as for example for planetary gears, friction (sleeve) bearings are often used. The cylindrical surfaces of the pin and rotating part lead, particularly at high rotational speeds, to an insufficient lubricating-film formation, since an oil cushion cannot form. Increasing the bearing clearance could help, but on the other hand would result in less true rotation. Especially in the case of toothed parts, less true rotation would in turn result in poor tooth engagement, consequent interfering noises, and finally damage to the tooth system.
For this reason, so-called multi-surface friction bearings are often used. Said bearings are distinguished by a noncircular bore shape. Instead of a closed circle, the bore consists of at least three, and usually more, separate pitch circles, which are distributed in the bore circumference. The radii of these pitch circles are larger by a certain amount than the inscribed circle which contacts all pitch circles. This form of construction assures for each friction surface which is formed by a pitch circle a narrowing lubricant gap and with it the formation of a lubricating wedge with pressure production simultaneously on all friction surfaces.
However, in the interest of a constant oil cushion for a rotating part, the position of the multi-surface profile should be constant with respect to the direction of the forces applied from outside, for example the forces applied by the toothed system.
Therefore, a basic purpose of this invention is to provide a bearing construction of the type described in the Oberbegriff, which has both the advantages of the multi-surface friction bearing and also minimizes the risk of seizure between the relatively rotating parts.
A simple reversal of the conventional multi-surface friction bearing, so as to apply the multi-surface profile to the stationary part (the pin or the like), will not be satisfactory. The usual construction, in which the part carrying the profile is made entirely or partially of a bearing metal, for example bronze, has the disadvantage that as the bearing heats up, the bearing clearance is reduced, due to the larger expansion coefficient of the bearing metal compared with steel. This causes further heating up of the bearing and, because of the thus-caused further bearing clearance reduction, the danger of bearing seizure exists. Furthermore, a bearing sleeve which is fixed on the pin or a coating of the bearing material on the pin would become loose as the bearing surfaces heat up.
Further advantages and characteristics of the invention can be taken from the following description.